The Vibro-Acoustic Coupling Analysis Of Internal Sound Field

Aero-engine combustion chamber works in the environment of high-temperature and high-strength noise. The sonic fatigue and thermal fatigue are easily happened, which can seriously affect the life of the combustion chamber, and even the whole aero-engine's life. Combustion instability not only affects the stability of the aero-engine work, but also caused the combustion chamber flame tube thin-walled structure sound-vibration coupled fatigue. And there are some connections between the acoustic mode and the combustion instability. Consequently, in order to improve the fatigue life of the combustion chamber flame tube, it is particularly important to analyze vibration, acoustic and vibro-acoustic coupling characteristics of the aero-engine annular chamber flame tubes. In this paper, by theoretical method and finite element method (FEM), its own vibration mode and acoustic mode is studied. Then the mode testing of sound field and vibration is completed too.In this paper, based on the acoustics mode equations of cylindrical inner field, acoustic mode equation of double-cylindrical internal field is derived. FEM modals of the two cases are established to verify the theoretical method. Then, a simplified test model is designed according to the size of real gas turbine's annual combustion chambers. Using the model, we take the acoustical test and the test result is verified by the FEM computation result. Then, relieving one end plate of the simplified test model, the open sound field's character is studied by the test method and boundary element method (BEM). The influence of flow field and temperature field on the internal sound field is studied by FEM. Based on Donnell-Mushtari's cylindrical shell theory, the simple supported cylindrical shell's mode shapes and its resonance frequencies are given. Then Matlab program is written to compute the harmonic response based on the mode superposition method and its result is verified by FEM. The structure's modes of the simplified test model are obtained by FEM and test method. The vibro-acoustic coupling theory based on the modal coupling theory is given. The coupling characters between the simple supported cylindrical shell and its enclosure are studied by FEM. In the end, the vibro-acoustic coupling characteristics of the simplified test model are studied by FEM and test method.The research of structure's vibration mode and the enclosure's acoustic mode and the coupling characters is of great engineering application values to analyze and solve the sonic fatigue problems that are in order to improve the structure dynamic strength.